The present invention relates to a test pattern projector which is used to make adjustments of television cameras.
The color television camera in a television broadcasting studio requires adjusting operations in order to attain a favorable color image quality immediately before using. The adjusting operations are carried out by using a test pattern projector built into the camera. A test pattern chart of the transmission type or reflection type in the projector is illuminated so as to direct the image of the chart to an image pickup apparatus comprising a dichroic prism system and three camera tubes; and the color control unit (CCU) is adjusted according to observations of the image thus formed.
One of the known test pattern projectors which is disclosed in non-examined Japanese Patent Appln. Publ. No. 54-120529 comprises three variable brightness light sources, with red, green and blue filters associated with the respective light sources and an optical element for mixing the red, green and blue light passing through the respective filters. In this projector, the color temperature of the illuminating light for the test pattern chart can be adjusted to the color temperature of about 3,000.degree. K of the illuminating light in broadcasting studio component ratio, by varying the intensity of the light sources through variable resistors connected with the respective light sources to regulate the component ratio of the red, green and blue light.
However it is difficult for the projector mentioned above to maintain a well-balanced component ratio of the illuminating light from said three sources, with the result that the adjustment of the color temperature of the illuminating light is too complicated. Moreover, when one of said three light sources is changed following a breakdown, a readjustment of color temperature must be made. In addition to this, the test pattern projector suffers from the further drawback that the illuminating light has differences in brightness for the center to the edge because of a scattered quantity distribution of light from the respective light source.